Inputs from the A1 noradrenergic region to hypothalamic paraventricular neurons in the rat

Catecholamines modulate differentially nonapeptide precursor mRNA expression in the preoptic area and ovary of the catfish Heteropneustes fossilis: An in vitro study

In the catfish Heteropneustes fossilis, three nonapeptide hormone genes were identified in the brain preoptic area (POA) and ovary: a pro-vasotocin (pro-vt) and two isotocin gene paralogs viz., a novel pro-ita and conventional pro-itb. In the present study, the regulatory role of catecholamines [CA: dopamine (DA), noradrenaline (NA), adrenaline (AD)] on the expression of these genes were investigated in vitro. DA (1, 10, and 100 ng/mL) inhibited significantly the mRNA expression in both the POA and ovary. NA upregulated the POA mRNA expression in a biphasic manner, the lower concentrations (1 ng and 10 ng) scaled up and the higher concentration (100 ng) scaled down the expression of pro-vt and pro-itb, while only the 1 ng NA scaled up the pro-ita expression. In the ovary, NA upregulated the mRNA expressions at all concentrations; the pro-vt expression was stimulated only at 10 and 100 ng. AD stimulated pro-vt and pro-ita expression in the POA at all concentrations but the pro-itb expression was inhibited at 1 and 10 ng, and stimulated at 100 ng concentrations. In the ovary, AD elicited varied effects; no significant change in pro-vt, a stimulation of pro-ita, and an inhibition of pro-itb at 1 ng, and stimulation of pro-itb at the 10 and 100 ng. The incubation of the POA and ovary with α-methylparatyrosine (MPT, 250 µg/mL, a tyrosine hydroxylase inhibitor) for 8 h downregulated the mRNA expression in the POA but unaltered the expression in the ovary. Pre-incubation with MPT for 4 h, followed by co-incubation with DA, NA or AD for 4 h elicited varied effects. In the POA, the co-incubations with the CAs rescued the inhibition due to MPT. The MPT + DA and MPT + AD treatments reduced the magnitude of the inhibition of pro-vt and pro-itb by MPT. But the pro-ita expression was modestly stimulated in the MPT + AD group. On the other hand, the MPT + NA treatment rescued the MPT effect and elicited 10-folds increase in the expression levels. In the ovary, the changes were: an inhibition in the MPT + DA group, no significant alteration in the MPT + NA group, and a mild stimulation in the MPT + AD group. The results suggest that CAs modulate brain and ovarian nonapeptide gene expression differentially, which is important in the neuroendocrine/endocrine integration of reproduction in the catfish.

Oxytocin Signaling Pathway: From Cell Biology to Clinical Implications

BACKGROUND

In addition to the well-known role played in lactation and parturition, Oxytocin (OT) and OT receptor (OTR) are involved in many other aspects such as the control of maternal and social behavior, the regulation of the growth of the neocortex, the maintenance of blood supply to the cortex, the stimulation of limbic olfactory area to mother-infant recognition bond, and the modulation of the autonomic nervous system via the vagal pathway. Moreover, OT and OTR show antiinflammatory, anti-oxidant, anti-pain, anti-diabetic, anti-dyslipidemic and anti-atherogenic effects.

OBJECTIVE

The aim of this narrative review is to summarize the main data coming from the literature dealing with the role of OT and OTR in physiology and pathologic conditions focusing on the most relevant aspects.

METHODS

Appropriate keywords and MeSH terms were identified and searched in Pubmed. Finally, references of original articles and reviews were examined.

RESULTS

We report the most significant and updated data on the role played by OT and OTR in physiology and different clinical contexts.

CONCLUSION

Emerging evidence indicates the involvement of OT system in several pathophysiological mechanisms influencing brain anatomy, cognition, language, sense of safety and trust and maternal behavior, with the possible use of exogenous administered OT in the treatment of specific neuropsychiatric conditions. Furthermore, it modulates pancreatic β-cell responsiveness and lipid metabolism leading to possible therapeutic use in diabetic and dyslipidemic patients and for limiting and even reversing atherosclerotic lesions.

Structural and functional diversity of nonapeptide hormones from an evolutionary perspective: A review

The article presents an overview of the comparative distribution, structure and functions of the nonapeptide hormones in chordates and non chordates. The review begins with a historical preview of the advent of the concept of neurosecretion and birth of neuroendocrine science, pioneered by the works of E. Scharrer and W. Bargmann. The sections which follow discuss different vertebrate nonapeptides, their distribution, comparison, precursor gene structures and processing, highlighting the major differences in these aspects amidst the conserved features across vertebrates. The vast literature on the anatomical characteristics of the nonapeptide secreting nuclei in the brain and their projections was briefly reviewed in a comparative framework. Recent knowledge on the nonapeptide hormone receptors and their intracellular signaling pathways is discussed and few grey areas which require deeper studies are identified. The sections on the functions and regulation of nonapeptides summarize the huge and ever increasing literature that is available in these areas. The nonapeptides emerge as key homeostatic molecules with complex regulation and several synergistic partners. Lastly, an update of the nonapeptides in non chordates with respect to distribution, site of synthesis, functions and receptors, dealt separately for each phylum, is presented. The non chordate nonapeptides share many similarities with their counterparts in vertebrates, pointing the system to have an ancient origin and to be an important substrate for changes during adaptive evolution. The article concludes projecting the nonapeptides as one of the very first common molecules of the primitive nervous and endocrine systems, which have been retained to maintain homeostatic functions in metazoans; some of which are conserved across the animal kingdom and some are specialized in a group/lineage-specific manner.

Paraventricular-coerulear interactions: role in hypertension induced by prenatal undernutrition in the rat

Rats submitted to fetal growth retardation by in utero malnutrition develop hypertension when adult, showing increased hypothalamic mRNA expression for corticotropin-releasing hormone (CRH) and increased central noradrenergic activity. As hypothalamic CRH serves as an excitatory neurotransmitter within the locus coeruleus (LC) and coerulear norepinephrine plays a similar role within the paraventricular nucleus (PVN) of the hypothalamus, we studied, in both normal and prenatally undernourished 40-day-old anesthetized rats, the effects of intra-LC microinjection of CRH and intra-PVN microinjection of the alpha(1)-adrenoceptor antagonist prazosin on multiunit neuronal activity recorded simultaneously from the two nuclei, as well as the effects on systolic pressure. Undernutrition was induced during fetal life by restricting the diet of pregnant mothers to 10 g daily, whereas mothers of control rats received the same diet ad libitum. At day 40 of postnatal life: (i) undernourished rats showed increased neuronal activity in the PVN and LC, as well as increased systolic pressure; (ii) intra-LC CRH stimulated LC and PVN neurons and increased systolic pressure only in normal rats; (iii) intra-PVN prazosin decreased LC and PVN neuronal activity and systolic pressure only in undernourished rats; and (iv) in normal rats, prazosin prevented the stimulatory effect of CRH only in PVN activity; in undernourished rats, prazosin allowed CRH to regain its stimulatory effects. The results point to the existence of an excitatory PVN-LC closed loop, which seems to be hyperactive in prenatally undernourished rats as a consequence of fetal programming; this loop could be responsible, in part, for the hypertension developed by these animals.

Distribution and acute stressor-induced activation of corticotrophin-releasing hormone neurones in the central nervous system of Xenopus laevis

In mammals, corticotrophin-releasing hormone (CRH) and related peptides are known to play essential roles in the regulation of neuroendocrine, autonomic and behavioural responses to physical and emotional stress. In nonmammalian species, CRH-like peptides are hypothesized to play similar neuroendocrine and neurocrine roles. However, there is relatively little detailed information on the distribution of CRH neurones in the central nervous system (CNS) of nonmammalian vertebrates, and there are currently no comparative data on stress-induced changes in CRH neuronal physiology. We used a specific, affinity-purified antibody raised against synthetic Xenopus laevis CRH to map the distribution of CRH in the CNS of juvenile South African clawed frogs. We then analysed stress-induced changes in CRH immunoreactivity (CRH-ir) throughout the CNS. We found that CRH-positive cell bodies and fibres are widely distributed throughout the brain and rostral spinal cord of juvenile X. laevis. Strong CRH-immunoreactivity (ir) was found in cell bodies and fibres in the anterior preoptic area (POA, an area homologous to the mammalian paraventricular nucleus) and the external zone of the median eminence. Specific CRH-ir cell bodies and fibres were also identified in the septum, pallium and striatum in the telencephalon; the amygdala, bed nucleus of the stria terminalis and various hypothalamic and thalamic nuclei in the diencephalon; the tectum, torus semicircularis and tegmental nuclei of the mesencephalon; the cerebellum and locus coeruleus in the rhombencephalon; and the ventral horn of the rostral spinal cord. To determine if exposure to an acute physical stressor alters CRH neuronal physiology, we exposed juvenile frogs to shaking/handling and conducted morphometric analysis. Plasma corticosterone was significantly elevated by 30 min after exposure to the stressor and continued to increase up to 6 h. Morphometric analysis of CRH-ir after 4 h of stress showed a significant increase in CRH-ir in parvocellular neurones of the anterior preoptic area, the medial amygdala and the bed nucleus of the stria terminalis, but not in other brain regions. The stress-induced increase in CRH-ir in the POA was associated with increased Fos-like immunoreactivity (Fos-LI), and confocal microscopy showed that CRH-ir colocalized with Fos-LI in a subset of Fos-LI-positive neurones. Our results support the view that the basic pattern of CNS CRH expression arose early in vertebrate evolution and lend further support to earlier studies suggesting that amphibians may be a transitional species for descending CRH-ergic pathways. Furthermore, CRH neurones in the frog brain exhibit changes in response to a physical stressor that parallel those seen in mammals, and thus are likely to play an active role in mediating neuroendocrine, behavioural and autonomic stress responses.

Noradrenergic regulation of prolactin secretion at the level of the paraventricular nucleus of the hypothalamus: functional significance of the alpha-1b and beta-adrenergic receptor subtypes

Previous research has demonstrated that in the Siberian hamster, both photoperiod and estrous cyclicity alter the profile of noradrenergic activity with the paraventricular nucleus of the hypothalamus (PVN), and that noradrenergic activity is correlated with changes in circulating levels of prolactin. Work from our laboratory has demonstrated an inhibitory role for norepinephrine (NE) acting at the alpha-2 receptor subtype within the PVN on serum prolactin levels; however, the functional significance of other adrenergic receptor subtypes on this system is unknown. The purpose of this study was to investigate the functional significance of the alpha-1b and beta-adrenergic receptor subtypes at the level of the PVN on circulating levels of prolactin. These experiments were performed in male Siberian hamsters using reverse microdialysis coupled with serial blood sampling. In Experiment 1, infusion of l-phenylephrine hydrochloride (alpha-1b agonist) initiated a dose-dependent increase in circulating prolactin, whereas infusion of chloroethylclonidine (alpha-1b antagonist) induced a significant dose-dependent decline in prolactin. In Experiment 2, intraparaventricular administration of propranolol (beta antagonist) initiated a significant increase in prolactin levels in a dose-dependent manner, whereas isoproterenol (beta agonist) induced a dose-dependent decline in prolactin. The results of this study indicate that both the alpha-1b and beta-adrenergic receptor subtypes have a significant role in regulating circulating levels of prolactin at the level of the PVN in the Siberian hamster.

Extrahypothalamic corticotropin-releasing hormone mediates (-)-nicotine-induced elevation of plasma corticosterone in rats

(-)-Nicotine activates the hypothalamic-pituitary-adrenal axis via an activation of the brainstem catecholaminergic neurons in rats. The present study was undertaken to clarify the mechanisms involved in the (-)-nicotine-induced activation of brainstem catecholaminergic neurons in anesthetized rats. Physostigmine (a cholinesterase inhibitor) (0.31 and 0.77 micromol/animal, i.p.) dose-dependently elevated plasma corticosterone in the presence of scopolamine (a muscarinic receptor antagonist) (2.3 micromol/animal, i.p.). (-)-Nicotine (250 and 500 nmol/animal, i.c.v.) dose-dependently elevated plasma corticosterone with concomitant noradrenaline release in the hypothalamic paraventricular nucleus. The (-)-nicotine (500 nmol/animal, i.c.v.)-induced elevation of corticosterone was abolished by phentolamine (an alpha-adrenoceptor antagonist) (0.66 micromol/animal, i.c.v.), and attenuated by (+/-)-sotalol (a beta-adrenoceptor antagonist) (0.97 micromol/animal, i.c.v.). The (-)-nicotine-induced increases of plasma corticosterone and hypothalamic noradrenaline release were abolished either by hexamethonium (a nicotinic acetylcholine receptor antagonist) (1.8 micromol/animal, i.c.v.), CP-154,526 (butyl-ethyl-[2,5-dimethyl-7-(2,4,6-trimethylphenyl)-7H-pyrrolo[2,3-d]pyrimidin-4-yl]amine) (a selective CRF-1 receptor antagonist) (1.3 micromol/animal, i.c.v.) or indomethacin (a cyclooxygenase inhibitor) (1.2 micromol/animal, i.c.v.). These results suggest that (-)-nicotine elevates plasma corticosterone by CRF-1 receptor- and prostaglandin-mediated noradrenaline release in the paraventricular nucleus in rats.

Activation by serotonin and noradrenaline of vasopressin and oxytocin expression in the mouse paraventricular and supraoptic nuclei

Noradrenaline and serotonin are known to control arginine-vasopressin (AVP) and oxytocin (OT) secretion in the systemic circulation. The aim of the current study was to investigate whether these monoamines are also able to influence AVP and OT expression in the paraventricular (PVN) and supraoptic nuclei (SON). To test this hypothesis, we used the Tg8 transgenic mice KO for the monoamine oxidase-A gene, which present high levels of noradrenaline and serotonin in the brain. AVP and OT expression were evaluated at peptide and mRNA levels by immunohistochemistry, enzyme immunoassay, and in situ hybridization. Compared with wild type, the amounts of AVP, OT, AVP mRNA, and OT mRNA were increased in the PVN and SON in Tg8 mice. To distinguish the respective contributions of noradrenaline and serotonin to these modifications, we treated Tg8 mice with a synthesis inhibitor of either catecholamines [alpha-methylparatyrosine (alpha-MPT)] or serotonin [parachlorophenylalanine (pCPA)]. Administration of alpha-MPT to Tg8 mice induced a decline in the amounts of AVP, OT, and their mRNA in the PVN and SON. The pCPA treatment in Tg8 mice was also associated with a decrease in OT expression in the PVN and SON and in AVP expression in the PVN, but not in the SON. These results suggest that noradrenaline may activate AVP and OT expression in the PVN and SON. Likewise, serotonin is proposed to stimulate AVP and OT expression in the PVN and only OT expression in the SON.

Catecholamine systems in the brain of vertebrates: new perspectives through a comparative approach

A comparative analysis of catecholaminergic systems in the brain and spinal cord of vertebrates forces to reconsider several aspects of the organization of catecholamine systems. Evidence has been provided for the existence of extensive, putatively catecholaminergic cell groups in the spinal cord, the pretectum, the habenular region, and cortical and subcortical telencephalic areas. Moreover, putatively dopamine- and noradrenaline-accumulating cells have been demonstrated in the hypothalamic periventricular organ of almost every non-mammalian vertebrate studied. In contrast with the classical idea that the evolution of catecholamine systems is marked by an increase in complexity going from anamniotes to amniotes, it is now evident that the brains of anamniotes contain catecholaminergic cell groups, of which the counterparts in amniotes have lost the capacity to produce catecholamines. Moreover, a segmental approach in studying the organization of catecholaminergic systems is advocated. Such an approach has recently led to the conclusion that the chemoarchitecture and connections of the basal ganglia of anamniote and amniote tetrapods are largely comparable. This review has also brought together data about the distribution of receptors and catecholaminergic fibers as well as data about developmental aspects. From these data it has become clear that there is a good match between catecholaminergic fibers and receptors, but, at many places, volume transmission seems to play an important role. Finally, although the available data are still limited, striking differences are observed in the spatiotemporal sequence of appearance of catecholaminergic cell groups, in particular those in the retina and olfactory bulb.

Activation of gastric afferents increases noradrenaline release in the paraventricular nucleus and plasma oxytocin level

Effects of electrical stimulation of the gastric vagal nerves on plasma levels of oxytocin (OXT) and arginine vasopressin (AVP) were examined in rats anesthetized with urethane. Electrical stimulation of the gastric vagal nerves increased the plasma levels of OXT, but not AVP. The concentrations of extracellular noradrenaline (NA) in the paraventricular nucleus (PVN) were measured by in vivo microdialysis in rats anesthetized with urethane. Electrical stimulation of the gastric vagal nerves evoked an increase followed by a slight decrease in the concentrations of NA. The responses of spontaneous firing magnocellular neurosecretory neurons in the PVN to both electrical stimulation of the gastric vagal nerves and intravenous (i.v.) administration of CCK-8 were examined. Most of the putative OXT-secreting cells recorded were excited by both electrical stimulation of gastric vagal nerves and i.v. administration of CCK-8. These results suggest that gastric vagal afferents activate the central noradrenergic system from the brainstem to the PVN and secretion of OXT.

Noradrenergic excitation of magnocellular neurons in the rat hypothalamic paraventricular nucleus via intranuclear glutamatergic circuits

Noradrenergic projections to the hypothalamus play a critical role in the afferent control of oxytocin and vasopressin release. Recent evidence for intrahypothalamic glutamatergic circuits prompted us to test the hypothesis that the excitatory effect of noradrenergic inputs on oxytocin and vasopressin release is mediated in part by local glutamatergic interneurons. The voltage response to norepinephrine (30-300 microM) was tested with whole-cell recordings in putative magnocellular neurons of the paraventricular nucleus (PVN) in hypothalamic slices (400 micrometers). Norepinephrine elicited an alpha1 receptor-mediated direct depolarization in 23% of the magnocellular neurons tested; however, the most prominent response, seen in 42% of the magnocellular neurons, was an alpha1 receptor-mediated increase in the frequency of EPSPs. The norepinephrine-induced increase in EPSPs was blocked by tetrodotoxin and by ionotropic glutamate receptor antagonists, suggesting that norepinephrine excited presynaptic glutamate neurons to cause an increase in spike-mediated transmitter release. The increase in EPSPs also was observed in a surgically isolated PVN preparation (64% of cells) and with microdrop applications of norepinephrine (1 mM, 33% of cells) and glutamate (0.5-1 mM, 28%) in the PVN, indicating that the norepinephrine-sensitive presynaptic glutamate neurons are located within the PVN. Biocytin injection and subsequent immunohistochemical labeling revealed that both oxytocin and vasopressin neurons responded to norepinephrine. Our data indicate that magnocellular neurons of the PVN receive excitatory inputs from intranuclear glutamatergic neurons that express alpha1-adrenoreceptors. These glutamatergic interneurons may serve as an excitatory relay in the afferent noradrenergic control of oxytocin and vasopressin release under certain physiological conditions.

Difference in topology and numbers of barosensitive catecholaminergic and cholinergic neurons in the medulla between SHR and WKY rats

We hypothesized that there may be a significant difference in the neuronal composition of the baroreceptor reflex pathway between normotensive Wistar Kyoto (WKY) and spontaneously hypertensive SHR rats. Using the double-immunoreactive (IR) method, the topology and numbers of barosensitive neurons that contain glutamate (Glu), glutamic acid decarboxylase (GAD), tyrosine hydroxylase (TH), phenylethanolamine N-methyltransferase (PNMT) and choline acetyltransferase (ChAT) were compared between the two strains. The control rats were sham-operated only for cannulation of the trachea and femoral artery/vein. The test rats were injected with the pressor agent phenylephrine to raise blood pressure and stimulate arterial baroreceptors. In both the control and test experiments, the c-Fos/Glu-, GAD-, TH- and PNMT-IR neurons were found in the nucleus tractus solitarii (NTS) and ventrolateral medulla (VLM), while the FosB/ChAT-IR neurons were found in the NTS, dorsal motor nucleus of the vagus (DMX) and nucleus ambiguus (AMB). In the control experiment, no significant difference in numbers was recognized in any of the double-IR neurons between the two strains. In the test experiment, the numbers of FosB/ChAT-IR neurons in the NTS, DMX and AMB were significantly smaller in SHR than in WKY. The numbers of c-Fos/TH-IR neurons in the caudal VLM were significantly larger in SHR than in WKY. These results suggest that a smaller number of barosensitive cholinergic neurons in the DMX and AMB in SHR causes the weaker baroreceptor-cardiac vagal reflex in SHR, and that a larger number of barosensitive catecholaminergic neurons in the caudal VLM in SHR are involved in the stronger baroreceptor-vasopressin reflex in SHR.

Estrogen modifies the baroreceptor-induced responses of supraoptic vasopressin neurons in the ovariectomized rat

Effects of estrogen (E2) and estrogen plus progesterone (EP) on the baroreceptor-induced response of the spontaneous discharge activity in the supraoptic (SON) vasopressin (AVP) neurons were examined in ovariectomized (OVX) female rats. An increase or a decrease in arterial blood pressure induced by intravenous injection of phenylephrine or nitroprusside, resulted in an inhibition or an acceleration of the discharge activity in the identified AVP neurons. The slopes that were derived from a least squares regression line for the arterial blood pressure and baroreceptor-induced responses of AVP neurons in both OVX + E2 and OVX + EP rats were statistically smaller (P < 0.05) than that in the control OVX rat. These results suggest a functional relationship between ovarian endocrine and autonomic functions in the female rat.

Ultrastructural study of phenylethanolamine-N-methyltransferase, corticotropin-releasing factor and neurotensin immunoreactive neurons in the external cuneate nucleus of the gerbil

The present study examined the existence of catecholamine-, corticotropin-releasing factor (CRF)- and neurotensin (NT)-containing neurons in the external cuneate nucleus (ECN) of the gerbil using single label pre-embedding immunocytochemistry in an attempt to shed light on the increasing evidence for autonomic involvement of the ECN. Peroxidase immunoreactivity of phenylethanolamine-N-methyl-transferase (PNMT), CRF or NT was identified in the heterogeneous population of the ECN neurons characterized by a deeply infolded nucleus. The label was localized in their somata, dendrites, myelinated axons and axon terminals. The immunolabelled dendrites were contacted by spherical (S) and flattened (F) types of presynaptic boutons containing spherical and flattened synaptic vesicles, respectively. The PNMT-labelled dendrites, however, were postsynaptic to an additional type of axon terminals containing pleomorphic (P) synaptic vesicles. Among the immunoreactive axon terminals, the PNMT-labelled boutons consisted of two types: S and F; in the CRF- and NT-labelled axon terminals, only the S type was observed. The catecholamine-containing ECN neurons differed from the CRF- and NT-immunoreactive neurons in their synaptic organization. The latter two were considered to be of the same cell population because of their similarities in ultrastructural features and synaptic relations. In view of a high frequency (48% for PNMT, 50% for CRF and 46% for NT) of the F-typed boutons associated with the three categories of immunolabelled neurons in the ECN, it is possible that they are under considerable inhibitory control. The presence of catecholamine, CRF and NT in the ECN suggests that the nucleus may be involved in the integration of proprioception-, exercise- or stress-evoked autonomic responses.

Changes in blood volume and pressure induce c-fos expression in brainstem neurons that project to the paraventricular nucleus of the hypothalamus

Immunohistochemistry for c-fos was combined with retrograde tracing techniques to study the effects of acute reductions in arterial blood pressure due to hemorrhage (HEM) in conscious rats on activated neurons in the brainstem nucleus of the tractus solitarius (NTS) or ventrolateral medulla (VLM) which project to the paraventricular nucleus (PVN) of the hypothalamus. In an attempt to separate blood pressure effects from those associated with changes in blood volume, a similar approach was used to study the effects of drug-evoked hypotension using peripheral infusions of sodium nitroprusside (NP). Few differences were found in patterns or numbers of activated neurons (Fos-immunoreactive) in the NTS or VLM after HEM or NP treatment; only in the NTS at the level of the area postrema were significantly higher numbers of neurons that expressed Fos found in NP rats. In addition, a large proportion of PVN-projecting neurons in the NTS and VLM was activated whereas many activated neurons in the NTS and VLM did not project to the PVN. These results show that a decrease in blood pressure leads to the activation of NTS and VLM neurons but that a change in blood volume does not activate significantly greater numbers of neurons in these areas that project to the PVN or to other targets. Whereas substantial numbers of neurons in the NTS and VLM appear to transmit cardiovascular information to the PVN, many others likely transmit this information to other central targets.

Involvement of the noradrenergic afferents from the nucleus tractus solitarii to the supraoptic nucleus in oxytocin release after peripheral cholecystokinin octapeptide in the rat

Activation of abdominal vagal afferents by peripheral injection of cholecystokinin octapeptide induces oxytocin release into the circulation. To test the hypothesis that cholecystokinin increases oxytocin release via activation of noradrenergic afferents from the brainstem, we injected rats with 5-amino-2,4-dihydroxy-alpha-methylphenylethylamine, a selective neurotoxin to noradrenergic fibres, into a lateral cerebral ventricle. The neurotoxin treatment reduced the noradrenaline content in the hypothalamus by 75% and reduced the oxytocin secretion in response to cholecystokinin by over 90%. In separate experiments, the neurotoxin was injected unilaterally in the vicinity of the supraoptic nucleus to test whether direct noradrenergic afferents to the supraoptic nucleus are involved in the response to cholecystokinin. The injection reduced the immunoreactivity for dopamine beta-hydroxylase in the supraoptic nucleus and significantly decreased the number of the supraoptic neurons expressing Fos-like protein after cholecystokinin but not after hypertonic saline. In further experiments, rhodamine-conjugated latex microspheres were injected into the supraoptic nucleus to retrogradely label afferent neurons, and the brains were processed with double-immunohistochemistry for tyrosine hydroxylase and Fos-like protein. In the C2/A2 but not the C1/A1 region of the brainstem, cholecystokinin increased the expression of Fos-like protein in the population of retrogradely-labelled catecholaminergic cells. In the C2/A2 region, the majority of retrogradely labelled cells expressing Fos-like protein after cholecystokinin were catecholaminergic. We conclude that noradrenergic afferents from the A2 but not from the A1 region of the brainstem to the hypothalamus mediate, at least in part, oxytocin release following cholecystokinin.

Stress, antidepressant drugs, and the locus coeruleus

This review presents a synthesis of a large body of seemingly inconsistent literature on the role of the locus coeruleus-norepinephrine (LC-NE) system and the corticotropin-releasing hormone (CRH)-median eminence system in mediating the CNS effects of stress and the therapeutic effects of antidepressant drugs. The clinical implications of these findings for the etiology and treatment of stress-related psychiatric disorders such as depression will be discussed.

Hemorrhage induces Fos immunoreactivity in rat medullary catecholaminergic neurons

In urethane anesthetized rats one hour after lowering the systolic blood pressure to 70-75 mmHg by withdrawing 3-4 ml of blood, Fos immunoreactivity (Fos-IR), confined to the cell nucleus, was detected bilaterally in numerous cells of the nucleus of the solitary tract (NTS) and ventrolateral medulla (VLM). A few Fos-IR neurons were observed in the lateral reticular nucleus, dorsal medullary reticular nucleus, spinal trigeminal nucleus, medial inferior olive, interfasciculus hypoglossi and paramedian rostral medulla. In sham-operated animals, a much smaller number of Fos-IR neurons were scattered in the NTS, VLM and other nuclei mentioned above. Double labeling with antisera to tyrosine-hydroxylase (TH) and phenylethanolamine-N-methyltransferase (PNMT) showed that 60% of TH-positive neurons in the NTS contained Fos-IR, and 70-80% of TH-positive neurons in the caudal VLM and 50-60% of PMNT-positive neurons in the rostral VLM expressed Fos-IR. Only a few TH- or PNMT-positive neurons in the C2, C3 (paramedian rostral medulla) areas and within the medial longitudinal fasciculus were Fos-IR. About 40% of PNMT/Fos-IR neurons in the rostral VLM contained the retrograde tracer fluorogold, which was injected (< 1 microliter) into the white matter dorsolateral to the intermediolateral cell column of T2-T3 segments 2 to 3 days prior to hemorrhagic experiments. Very few TH-positive neurons in the caudal VLM contained fluorogold. Finally, clusters of Fos-IR neurons, which also labeled with antisera to choline acetyltransferase, were detected in the intermediolateral cell column of the spinal cord. The results indicate that during hemorrhage aminergic neurons in the caudal and rostral VLM and in the NTS are activated insofar as c-fos expression is concerned. As a corollary, the monoaminergic neurons in the medulla constitute an essential component in the ascending as well as descending reflex pathway involved in the adjustment of cardiovascular dynamics during hemorrhage.

CCK-8 excites oxytocin-secreting neurons in the paraventricular nucleus in rats--possible involvement of noradrenergic pathway

Systemic administration of CCK-8 increased plasma oxytocin (OXT) level in rats anesthetized with a mixture of urethane and alpha-chloralose. Extracellular recordings were made from magnocellular neurosecretory neurons in the paraventricular nucleus (PVN) of the hypothalamus in anesthetized rats to examine the effects of CCK-8 on the firing of PVN neurons. Thirteen out of 16 nonphasic neurons (putative OXT-secreting neurons) were excited by intravenous and/or intraperitoneal administration of CCK-8. By contrast, 8 out of 10 phasic cells, vasopressin(AVP)-secreting cells, were inhibited by systemic administration of CCK-8. Four out of five nonneurosecretory neurons in the PVN were excited by the administration of CCK-8. Moreover, microiontophoretically applied phentolamine blocked the excitatory responses induced by CCK-8 in nonphasic neurons. We measured extracellular noradrenaline (NA) level in the PVN, using in vivo microdialysis. Intravenous administration of CCK-8 induced NA release in the PVN. These results suggest that CCK-8 activates the excitatory afferent pathway to putative OXT-secreting neurons in the PVN which may, at least in part, be involved in the central noradrenergic projection.

Regional haemodynamic effects of noradrenaline injected into the hypothalamic paraventricular nuclei of conscious, unrestrained rats: possible mechanisms of action

The cardiovascular effects of noradrenaline bilaterally injected into the hypothalamic paraventricular nuclei were investigated in conscious, unrestrained Long-Evans rats and homozygous, vasopressin-deficient Brattleboro rats, chronically instrumented with pulsed Doppler probes for measurement of regional haemodynamics. In Long-Evans rats, incremental doses of noradrenaline (0.01-10 nmol) caused dose-related increases in blood pressure and a substantial, dose-related, superior mesenteric vasoconstriction. These changes were accompanied by bradycardia and reductions in renal and hind-quarter vascular conductances. In Brattleboro rats, noradrenaline (10 nmol) had no effect on blood pressure, heart rate, or renal or superior mesenteric vascular conductances. However, there was a slight vasodilatation in the vascular bed of the hindquarters. In Long-Evans rats, intravenous pretreatment with phentolamine had no effect on the bradycardia but partly inhibited the pressor response to noradrenaline injected into the paraventricular nuclei. These effects were associated with a smaller superior mesenteric vasoconstriction and an abolition of the vasoconstriction in the hindquarters. Combined intravenous pretreatment with phentolamine and propranolol had no effect on the heart rate or pressor responses to noradrenaline injected into the paraventricular nuclei, but reduced the superior mesenteric vasoconstriction, potentiated the vasoconstriction in the hindquarters and eliminated the renal vasoconstriction. These results suggest that, in untreated Long-Evans rats, alpha-adrenoceptor-mediated constriction in the mesenteric vascular bed and beta-adrenoceptor-mediated dilatation in the vascular bed of the hindquarters have important influences on the pressor response to noradrenaline injected into the paraventricular nuclei. In the presence of the vasopressin V1-receptor antagonist, d(CH2)5[Tyr(Et)]DAVP, the pressor and heart rate responses to noradrenaline injected into the paraventricular nuclei were abolished, as were the vasoconstrictions in the renal, superior mesenteric and hindquarter vascular beds. Together these results suggest an interaction between the sympathoadrenal system and vasopressin-mediated mechanisms in the cardiovascular responses to noradrenaline injected bilaterally into the paraventricular nuclei of conscious, untreated rats.

Catecholaminergic projections to tuberoinfundibular neurones of the paraventricular nucleus: III. Effects of adrenoceptor agonists and antagonists

Stimulation of the ventral noradrenergic ascending bundle (VNAB) at low frequencies (0.5/5 Hz) excited the majority (37/46, 80%) of single paraventricular nucleus (PVN) tuberoinfundibular neurones, with high frequency (50 Hz) trains of stimuli reversing the direction of the response to inhibition for 7/16 (44%) of these excited cells. Iontophoretic application of noradrenaline, or the alpha 1-adrenoceptor agonist 1-phenylephrine, increased the spontaneous electrical activity of most of the cells tested (94% and 72%), whilst application of the alpha 1-antagonist, ergotamine reduced the spontaneous activity of 44% of the cells tested and prevented the excitation following VNAB stimulation for 84% of the cells examined. Application of the beta-adrenoceptor antagonist, propranolol, increased the spontaneous activity of 77% of cells and prevented the inhibitory PVN neuronal responses following high frequency VNAB stimulation of 94% of the cells, often reversing the response to excitation similar to that observed following low frequency VNAB stimulation. The alpha 2-adrenoceptor antagonist, tolazoline, was found to evoke mixed responses from the cells examined but a trend towards a suppression of spontaneous activity and potentiation of VNAB stimulation-evoked responses was observed. The alpha 2-adrenoceptor agonist, clonidine, elicited an initial excitation from the majority of cells tested, with most of the cells then exhibiting an inhibition, either with or without continued application. Excitatory responses following stimulation of the sciatic nerve were recorded from the majority of cells (82.5%) and ergotamine was able to suppress this response for all four cells so tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Mapping study of noradrenergic stimulation of vasopressin release

The precise role of hypothalamic norepinephrine (NE) in the control of vasopressin (AVP) release has remained unclear, due to reports of both inhibitory and excitatory effects of NE and only a few studies with direct hypothalamic manipulations. The present study utilized a chronically implanted swivel brain cannula to investigate, in undisturbed and freely behaving rats, the impact of acute hypothalamic infusions of monoamines on circulating AVP levels. The first study examined and compared the responsiveness of six hypothalamic sites to NE infusion through the swivel cannula. Results indicated that the excitatory effect of central noradrenergic stimulation on serum AVP is highly site specific, localized to the paraventricular (PVN) and supraoptic (SON) nuclei. These two nuclei appeared to be equally responsive to NE infusion, yielding a threefold rise in serum AVP over baseline levels. In contrast, NE in the dorsomedial nucleus produced a significantly smaller increase in AVP, and no response was observed in the ventromedial nucleus, posterior hypothalamus, or perifornical lateral hypothalamus. Further tests conducted in the PVN showed this nucleus to respond in a dose-dependent manner to NE infusion. In contrast, under similar test conditions, dopamine caused only a small increase in AVP at a relatively high dose, while a PVN injection of serotonin produced no response. These results support the existence of an excitatory noradrenergic system controlling AVP release and specifically demonstrate that this function of NE is localized to the PVN and SON, in contrast to other hypothalamic areas, and is mimicked to some extent by dopamine but not by serotonin.

Collateral input to the paraventricular and supraoptic nuclei in rat. II. Afferents from the ventral lateral medulla and nucleus tractus solitarius

In the rat, medullary afferents to the hypothalamic magnocellular nuclei mediate the baroreceptor reflexes of vasopressinergic neurons and the cholecystokinin- or gastric distention-induced excitation of oxytocinergic neurons. One strategy that reflexes such as these may use to coordinate the activity of magnocellular neuroendocrine neurons is collateral branching of input. Previous work has shown that the distributions of medullary neurons projecting to the paraventricular and the supraoptic nuclei overlap and that their axons branch. Thus, we hypothesized that single neurons in the ventral lateral medulla and/or the nucleus tractus solitarius would project to both the paraventricular and supraoptic nuclei via collateral branches of their axons. Medullary afferent neurons were retrogradely labeled after injection into the paraventricular and the supraoptic nucleus on one side of the brain with two different fluorescent tracers: Fluoro-Gold or rhodamine-labeled latex microspheres. The topographic distribution of labeled cells in the medulla containing either a single fluorescent tracer or both tracers were plotted. Of these labeled neurons, a small percentage (7%) contained both dyes, suggesting that they send collateral branches to both of the magnocellular neuroendocrine nuclei injected. Single labeled cells were both ipsi- and contralateral to the injected side (53% ipsilateral), but most double-labeled cells were ipsilateral (84%). In rats, areas that project to both the paraventricular and the supraoptic nuclei may act upon both nuclei together. Thus, afferent inputs, in conjunction with the known inter- and intracellular changes that take place within the magnocellular nuclei, may be involved with the coordinated responses throughout magnocellular neuroendocrine system during medullary reflexes, i.e., the baroreceptor-mediated reflexes or the gastric distention reflexes.

Excitation of supraoptic vasopressin cells by stimulation of the A1 noradrenaline cell group: failure to demonstrate role for established adrenergic or amino acid receptors

The effects of adrenergic and excitatory amino acid antagonists on supraoptic nucleus (SON) neurosecretory cell responses to stimulation of the A1 noradrenaline (NA) cell group were examined in anaesthetized male rats. As in previous studies, delivery of cathodal pulses (100 microA, 1 ms pulses, 1 Hz) to the A1 region of the caudal ventrolateral medulla excited spontaneously active, antidromically identified neurosecretory cells, the majority of which were identified as arginine vasopressin (AVP) secreting on the basis of basal discharge patterns and responses to abrupt increases in arterial blood pressure. Administration of alpha- and beta-adrenoreceptor antagonists, by systemic or intracerebroventricular delivery of a bolus, or by direct pressure injection into the SON, did not alter neurosecretory cell responses to A1 stimulation, even when doses applied exceeded that required for blockade of excitations elicited by local application of NA. Application of the broad spectrum excitatory amino acid antagonist kynurenic acid (5-40 mM) blocked the excitatory effects of locally applied glutamate (100 microM) and transiently inhibited spontaneous activity, but failed to alter the excitatory effects of A1 region stimulation on SON cells. Identical effects were obtained with a selective kainate/quisqualate receptor antagonist. These data indicate that neurosecretory cell responses to activation of the A1 cell group are unaltered by antagonists of alpha- and beta-adrenoreceptors, or excitatory amino acid receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of neurotransmitters in the central regulation of the cardiovascular system

The last decade has seen tremendous progress in determining the nature of the neurotransmitters which regulate central nervous system pathways involved in the regulation of blood pressure. Investigations are now pursuing the identity and functional importance of neurotransmitters contained within pathways shown to be important in cardiovascular regulation. In addition, several key components of the brain stem networks involved in the control of sympathetic activity have been identified. For example, numerous studies indicate the importance of neurons located in the rostral ventrolateral medulla in the regulation of SPN. Indeed, this area contains medullospinal sympathoexcitatory neurons which represent the final site of integration of many brain stem and reflex pathways involved in the regulation of sympathetic nerve activity. The neurotransmitter which is utilized by this medullospinal pathway remains unknown. Epinephrine, substance P and glutamate have all been hypothesized as primary chemical mediators in the descending pathway from the brain stem to SPN. Interestingly, lesions of, or antagonists to, epinephrine, substance P, glutamate and 5-HT neurons all abolish sympathetic activity and reduce blood pressure to a level similar to that in a spinal animal. Clearly, not all these transmitters are primary mediators of sympathetic information carried from the brain stem to the spinal cord. It is likely that monoamines and neuropeptides act in the IML, as in other area of the central nervous system, as neuromodulators to set the level of excitability of SPN rather than relaying sympathetic information over a functionally specific medullospinal pathway. This conclusion is supported by the observation that midline medullary 5-HT neurons provide a tonic excitatory input to SPN, but receive no afferent inputs from other central sympathetic or baroreceptor pathways. However, the firing of 5-HT neurons appears to relate to the state of vigilance of the animal. This suggests that 5-HT neurons may lower the threshold of SPN to sympathetic inputs during states of wakefulness. In addition, the time course of the norepinephrine-mediated slow EPSPs and IPSPs in SPN is consistent with a gain-setting function. By analogy, epinephrine is likely to act as a neuromodulator in the IML rather than to serve as the primary mediator of sympathetic information descending from the rostral ventrolateral medulla.(ABSTRACT TRUNCATED AT 400 WORDS)

Emerging concepts of structure-function dynamics in adult brain: the hypothalamo-neurohypophysial system

As the first known of the mammalian brain's neuropeptide systems, the magnocellular hypothalamo-neurohypophysial system has become a model. A great deal is known about the stimulus conditions that activate or inactivate the elements of this system, as well as about many of the actions of its peptidergic outputs upon peripheral tissues. The well-characterized actions of two of its products, oxytocin and vasopressin, on mammary, uterine, kidney and vascular tissues have facilitated the integration of newly discovered, often initially puzzling, information into the existing body of knowledge of this important regulatory system. At the same time, new conceptions of the ways in which neuropeptidergic neurons, or groups of neurons, participate in information flow have emerged from studies of the hypothalamo-neurohypophysial system. Early views of the SON and PVN nuclei, the neurons of which make up approximately one-half of this system, did not even associate these interesting, darkly staining anterior hypothalamic cells with hormone secretion from the posterior pituitary. Secretion from this part of the pituitary, it was thought, was neurally evoked from the pituicytes that made the oxytocic and antidiuretic "principles" and then released them upon command. When these views were dispelled by the demonstration that the hormones released from the posterior pituitary were synthesized in the interesting cells of the hypothalamus, the era of mammalian central neural peptidergic systems was born. Progress in developing an ever more complete structural and functional picture of this system has been closely tied to advancements in technology, specifically in the areas of radioimmunoassay, immunocytochemistry, anatomical tracing methods at the light and electron microscopic levels, and sophisticated preparations for electrophysiological investigation. Through the judicious use of these techniques, much has been learned that has led to revision of the earlier held views of this system. In a larger context, much has been learned that is likely to be of general application in understanding the fundamental processes and principles by which the mammalian nervous system works.(ABSTRACT TRUNCATED AT 400 WORDS)

Catecholaminergic projections to tuberoinfundibular neurones of the paraventricular nucleus: I. Effects of stimulation of A1, A2, A6 and C2 cell groups

Extracellular electrical activity was recorded from 203 paraventricular nucleus (PVN) neurones antidromically identified as projecting to the median eminence. Spontaneous activity and the effects of stimulation of the A1, A2, A6 and C2 catecholaminergic cell groups upon the PVN neurones were examined. Cells were located at a mean height 2.29 +/- 0.03 mm above the base of the brain, corresponding with the corticotropin-releasing factor (CRF) rich component of the nucleus. The mean firing rate was 3.2 +/- 0.3 Hz and antidromic invasion latency was 9.9 +/- 0.3 msec. Seventy-six % of cells tested were activated by painful somatosensory stimuli. Electrical stimulation of the A1 or A2 region evoked excitatory responses from the majority of cells tested (76% and 85%, respectively), whilst stimulation of the A6 and C2 regions evoked more inhibitory responses (43% and 59%, respectively). Most responses (56%), whether excitatory or inhibitory, were not clearly defined in terms of latency, and were only observed following delivery of 5-10 single shocks at 0.5 Hz. Excitation recorded following A1 and A2 stimulation suggests a facilitatory role for noradrenaline in the regulation of PVN activity. Inhibitory responses following C2 stimulation indicate that adrenaline may serve to inhibit such activity, whilst the more mixed responses following A6 stimulation suggest that the projections of this region differ in some way from those of the A1 and A2 cells. Response reversals were observed, after delivery of higher frequency stimulation, for a substantial proportion (20%) of the cells tested.

Catecholaminergic projections to tuberoinfundibular neurones of the paraventricular nucleus: II. Effects of stimulation of the ventral noradrenergic ascending bundle: evidence for cotransmission

In order to further elucidate the neural mechanisms underlying the control of adrenocortical secretion, responses of paraventricular nucleus (PVN) tuberoinfundibular neurones were examined following stimulation of the ventral noradrenergic ascending bundle (VNAB). Stimulation at low frequencies (0.5/5 Hz) excited the majority (52/64, 81%) of cells but only 15 showed a clear-cut, stimulus-locked, activation with onset latency of 44.5 +/- 10.0 msec and offset at 71.9 +/- 11.3 msec: the remaining 37 excited cells showed overall increases in firing after delivery of 5-10 stimuli. High frequency (50 Hz) trains of stimuli reversed the direction of response to inhibition for 14/52 of the excited cells. Inhibition of (nor)adrenaline synthesis by alpha-methylparatyrosine was without effect upon the firing of cells examined or the distribution and latencies of their responses following low frequency stimulation; high frequency trains reversed the response direction of only 4/35 cells, (p less than 0.05 vs. control rats; chi 2-test). Intracerebroventricular administration of 6-hydroxydopamine, a catecholaminergic neurotoxin, reduced the proportion of cells excited by the stimulation (10/47; p less than 0.005; chi 2-test). Unit responses to painful somatosensory stimuli were recorded from the majority of the cells tested (74%), except following 6-hydroxydopamine treatment, when only 38% were excited (p less than 0.005; chi 2-test). The results demonstrate that the VNAB provides an excitatory input to the PVN and that noradrenaline is probably responsible for this effect but a cotransmitter (neuropeptide Y?) may also be responsible for the observed excitatory responses. Inhibitory responses following high frequency stimulation were probably also mediated by (nor)adrenaline.(ABSTRACT TRUNCATED AT 250 WORDS)

Paraventricular nucleus injections of noradrenaline: cardiovascular effects in conscious Long-Evans and Brattleboro rats

The cardiovascular effects of noradrenaline injected into the hypothalamic paraventricular nucleus (PVN) were investigated in conscious Long-Evans (control) rats and homozygous vasopressin (AVP)-deficient Brattleboro rats. Unilateral microinjection of noradrenaline (3-30 nmol) into the PVN produced dose-dependent increases in systolic and diastolic blood pressure of Long-Evans rats, and a concomitant decrease in heart rate. Only the highest dose of noradrenaline tested (30 nmol) caused a significant pressor response in Brattleboro rats (9 +/- 4/9 +/- 4 mm Hg, systolic/diastolic, n = 7) which was significantly smaller than the response produced by the same dose of noradrenaline in Long-Evans rats (32 +/- 8/27 +/- 6 mm Hg, n = 7). Intravenous pretreatment of Long-Evans rats with the V1-receptor antagonist, d(CH2)5Tyr[Et]DAVP, almost completely abolished the pressor effect of noradrenaline (10 nmol) without significantly attenuating the bradycardia. The alpha 2-adrenoceptor antagonist, idazoxan (4 nmol), injected into the PVN abolished the pressor response produced by noradrenaline (10 nmol) in Long-Evans rats but had no significant effect on the bradycardia. Pretreatment with the alpha 1-adrenoceptor antagonist, prazosin (0.7 nmol), significantly attenuated both the pressor and bradycardic effects of noradrenaline in Long-Evans rats. These results suggest that the pressor response produced by microinjection of noradrenaline into the hypothalamic PVN of conscious Long-Evans rats is mediated largely through stimulation of alpha 2-adrenoceptors and is dependent, in part, on release of AVP into the circulation. A component of the bradycardia seen with this intervention may be mediated through stimulation of alpha 1-adrenoceptors in the PVN.

Corticotropin-releasing factor release from in vitro superfused and incubated rat hypothalamus. Effect of potassium, norepinephrine, and dopamine

We have compared the release of CRF induced by potassium depolarization, noradrenaline or dopamine as monitored either during superfusion of mediobasal hypothalamus or during incubation of whole hypothalamus. The superfusion device was improved in order to prevent gas leakage and to keep constant pO2 and pCO2 in the superfusion chamber. Basal CRF secretion as well as KCl- and norepinephrine-induced CRF release were comparable in superfusion and incubation experiments. Pharmacological investigations suggest that the stimulatory effect of norepinephrine on CRF release is mediated mainly through alpha 1 and alpha 2 adrenergic receptors, and partially through beta receptors.

Re-evaluation of the effects of norepinephrine on the single-unit activity of paraventricular neurosecretory neurons

Electrical stimulation of the A1 noradrenergic region elicited predominantly an excitatory orthodromic response from paraventricular neurosecretory neurons recorded in urethane-anesthetized male rats. In a majority of cases, locally applied norepinephrine (NE) as well as A1 region stimulation excited paraventricular neurosecretory neurons. However, in some neurons including a subpopulation of putative vasopressin neurons, iontophoresed NE was inhibitory. Both excitatory and inhibitory effects of NE were selectively blocked by the alpha-antagonist, phentolamine, but not by the beta-antagonist, timolol. In general, the results support the notion that the A1 noradrenergic input to paraventricular neurosecretory neurons is excitatory. Nevertheless, the results do not exclude the possibility that NE exerts a specific, alpha-receptor-mediated, inhibitory effect on a subpopulation of paraventricular neurons.

Inhibitory effect of norepinephrine on the single-unit activity of caudally projecting paraventricular neurons

The role of norepinephrine (NE) in controlling the single-unit activity of paraventricular (PVN) neurons projecting to or passing through the caudal ventrolateral medulla (CVLM) was investigated in adult male rats anesthetized with urethane. Of 72 PVN neurons studied, 19 were antidromically activated by CVLM stimulation (Group I) and 48 were antidromically activated by posterior pituitary (PP) stimulation (Group II). The remaining 5 neurons were antidromically driven by both CVLM and PP stimulation (Group III). In 14 of the 19 Group I neurons and in all the 5 Group III neurons, iontophoretically applied NE was demonstrated to be inhibitory to the single-unit activity. No excitatory effect of NE was observed. In contrast, both excitatory and inhibitory actions of NE were observed in the Group II neurons. Of 37 Group II neurons tested, 28 were excited and 7 were inhibited by NE. The inhibitory effect of NE in Group I and Group III neurons was selectively blocked by the alpha antagonist, phentolamine, that was coiontophoresed with NE, but not by the beta antagonist, timolol (n = 9). The unit activity of Group I neurons that were inhibited by NE was not altered by an increase in arterial blood pressure (n = 3), whereas the unit activity of one NE-insensitive Group I neuron was decreased by an increase in blood pressure. Taken together, the results suggest that NE plays an alpha-adrenoreceptor-mediated inhibitory role in controlling the single-unit activity of caudally projecting PVN neurons. These neurons include a subpopulation of PVN neurons that project caudally as well as to the PP. The possible function associated with the NE-sensitive, caudally projecting PVN neurons may be other than the regulation of blood pressure.

Catecholaminergic neurons in the ventrolateral medulla and nucleus of the solitary tract in the human

Catecholaminergic neurons in the ventrolateral medulla (VLM) and nucleus of the solitary tract (NTS) are important because of their presumed roles in autonomic regulation, including the tonic and reflex control of arterial pressure, neuroendocrine functions, and the chemosensitivity associated with the ventral medullary surface. However, little is known about the connections of these neurons in the human brain. As a first step in analyzing the functional biochemical anatomy of catecholamine neurons in the human, we used antisera against tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT) to localize medullary catecholamine-containing neurons and processes in the VLM and the NTS. Cells staining for TH were located throughout the VLM. Most cells staining for TH and PNMT, which are therefore adrenergic, occurred in an area of the VLM probably corresponding to the rostroventrolateral reticular nucleus. Axons of TH-immunoreactive neurons in the VLM projected (1) dorsally, in a series of parallel transtegmental trajectories, toward the dorsomedial reticular formation, the NTS, and vagal motor nucleus, (2) longitudinally, through the central tegmental field, as fascicles running parallel to the neuraxis, (3) ventrolaterally toward the ventral surface (VS) of the rostral VLM where they appeared to terminate, and (4) medially into the raphe, where they arborized. Similar systems of fibers were labeled for PNMT; the longitudinal bundles of PNMT-labeled axons were limited to the principal tegmental bundle and concentrated dorsally. Fibers containing PNMT were also identified in the medullary raphe, on the medullary ventral surface, and contacting intraparenchymal blood vessels. In the NTS, neurons exhibited immunoreactivity to both TH and PNMT: Four principal subgroups of TH-immunoreactive neurons were seen: a ventral, an intermediate, a medial, and a dorsal group. Perikarya containing PNMT were restricted to the dorsolateral aspect of the NTS. Processes containing TH and PNMT immunoreactivity were identified in the medial and dorsolateral NTS; others appeared to project between the NTS and the VLM and within the solitary tract. The presence of catecholaminergic fibers of the VLM interconnecting with the NTS, raphe, intraparenchymal microvessels, VS, and possibly the spinal cord suggests that the autonomic and chemoreceptor functions attributed to these neurons also may apply to the human.

Organization of central adrenergic pathways: I. Relationships of ventrolateral medullary projections to the hypothalamus and spinal cord

We studied the organization of projections from the C1 adrenergic and A1 noradrenergic cell groups in the ventrolateral medulla (VLM) to the hypothalamus and the spinal cord by using a combination of retrograde transport of fluorescent tracers and immunocytochemistry. Three issues were addressed. Neurons in the VLM that stain immunohistochemically for phenylethanolamine N-methyltransferase (PNMT) have been assumed to be adrenergic. However, the presence of PNMT-immunoreactive neurons in the hypothalamus that do not stain for tyrosine hydroxylase (TH) prompted us to re-evaluate the VLM by an elution-restaining immunohistochemical procedure. We confirmed that nearly all of the rostral medullary PNMT-immunoreactive neurons also stained for TH. By contrast, in the caudal medulla, very few TH-positive neurons stained for PNMT. Neurons of the C1 group in the rostral VLM project both to the thoracic spinal cord and to the hypothalamus. To determine whether individual C1 neurons send collaterals to the hypothalamus and spinal cord, we injected different-colored fluorescent dyes (diamidino yellow or fast blue) into the thoracic spinal gray matter and either the median preoptic (MnPO) or paraventricular (PVH) nuclei of the hypothalamus. Very few double-labeled neurons were found in the VLM, indicating that hypothalamic and spinal cord projections arise from almost completely independent populations of cells. Approximately half of the neurons projecting to the spinal cord from rostral VLM were not immunoreactive for TH or PNMT, indicating that a substantial part of this projection is noncatecholaminergic. The MnPO and the PVH both receive extensive catecholaminergic inputs from the VLM. We also used fluorescent retrograde tracers to determine whether individual VLM neurons send collaterals to both hypothalamic sites. Approximately 20% of neurons projecting to the MnPO in the rostral two thirds of the VLM also sent collaterials to the PVH, nearly all of these neurons being TH-positive. The collateralization of the VLM catecholaminergic projection to the hypothalamus may provide an anatomical substrate for integration of fore-brain participation in cardiovascular regulation. In contrast, the adrenergic projection from the VLM to the intermediolateral column of the spinal cord arises from a separate population of neurons.

Neuropeptide Y injected into the supraoptic nucleus causes secretion of vasopressin in the unanesthetized rat

Injection of neuropeptide Y (NPY, 0.01-1.0 nmol in 0.25 microliter vehicle) into the supraoptic nucleus of unanesthetized rats increased plasma vasopressin, measured by radioimmunoassay, to a maximum of 90 +/- 18 ng/liter. Injections of vehicle or somatostatin did not increase plasma vasopressin, nor did injections of NPY into the amygdala. Double-labelling immunohistochemical studies demonstrated that fibers containing NPY-like immunoreactivity form a close association with vasopressin immunoreactive perikarya in the supraoptic nucleus. It appears that NPY may directly excite vasopressin-containing neurons causing secretion of vasopressin.

Potential disynaptic pathways connecting the fastigial pressor area and the paraventricular nucleus of the hypothalamus in the rat

Efferents from the cardiovascular portion of the fastigial nucleus (rFN), whose electrical stimulation has been found to elicit secretion of vasopressin in the rat, have been traced by use of the anterograde fluorescent tracer Fast blue (FB). In the same animal the retrograde marker Diamidino yellow (DY) was injected in the paraventricular nucleus of the hypothalamus (PVH) to trace afferents to the neurosecretory cells of the hypothalamus. Frontal sections of the brainstem have been analyzed and the FB-labeled axons and terminals and the DY-labeled cells mapped. Both efferents from the rFN and cells projecting to the PVH were found in close contact in the region of the locus coeruleus and parabrachial nucleus (lateral division) and in the caudal ventrolateral medulla, dorsal to the lateral reticular nucleus. Those two regions may function as putative relay stations of disynaptic pathways linking the rFN to the PVH.